1. Field of the Invention
The present invention relates to an improvement in the structure of a temperature sensitive hydraulic coupling of the type in which the rotation of the automobile engine cooling fan is automatically controlled by sensing the variation of ambient temperature depending on the travelling condition of the automobile so that a suitable amount of cooling air is supplied to the engine.
2. Description of the Prior Art
Conventionally, the above type of cooling fan coupling has been constructed such that as shown in FIGS. 9 and 10, a plurality of communication holes 27' are provided in a drive disk 27 (corresponding to the essential portion of the present invention) and the rotation of the fan is controlled only by adjusting the flow of oil from an oil chamber 26 to a torque transmission chamber 24.
However, the above-mentioned prior art technology has had such disadvantages that since it relies on a torque transmission mechanism based on the variation of the ambient temperature, the amount of cooling air to be supplied to the engine becomes too large by excessive rotation of the fan as shown by the curve B of FIG. 6a at the time of high speed rotation of the engine during high speed travelling of the automobile for which not so much amount of cooling air by the fan is required and further, the number of revolutions of the fan also increases due to a rapid increase in the number of revolutions of the drive shaft as shown by the curves Bs of FIGS. 6b and 6c with respect to cases in which the engine is accelerated with a large and a small speed difference with respect to the normal travelling speed of the automobile so that the primary object of the fan coupling, that is, the reduction of the amount of horsepower consumption and fan noise level, is not fully achieved leaving a room for further improvement.